Quote:
Originally Posted by Troy
Thanks Ray,
you have given me plenty of ideas
Yeah after I wrote my last post I then thought that the mean would be the best way to go not sure how much the max histogram value would jump around indoors.
In my last post I wrote
>>Also, would it be better to have the same exposure and gain settings and adjust the light source distance so they have the same histogram value?
I think if it was done this way the only difference would be the noise value without having done this myself it seems like a good way for the SNR test.
For another signal test I thought about screwing different filters onto the camera's, such as red, green and blue while pointing it at a white light source. It would be interesting to compare the different channels particularly the blue because this wavelength struggles with signal on some of the planets and as a result a lower frame rate is used.
Thanks again Ray I like your real world testing.
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It sure is an interesting task and I would be keen to know what you find on the colour evaluation. I went into it thinking that it would be relatively easy to just do a simple test and compare cameras, but it turned out to quite difficult to ensure that the comparison was fair and that the results were realistic enough actually mean something to someone trying to image Saturn.
A few things that I found and that you might consider:
1. the cameras I tested have quite different internal gains (adu/photon), so using the same nominal gain setting in Firecap will set the cameras up differently and you won't be comparing apples with apples - in particular, the histogram values for different cameras will not mean the same thing in your test method. To get around this, I used a constant and realistic illumination to ensure that the light input per pixel was constant, and then compared the outputs at various gain and exposure settings - that way at least the input was fixed in an absolute sense.
2. the cameras have different pixel sizes. In use the Fno of the optics would be varied to get the same pixel scale for each camera and you need to adjust the source distance so that the pixel illumination reflects the effect of the real-world variation in the Fno of the optics - for an unfocused source, the distance must be adjusted in proportion to the pixel linear dimensions in order to get an apples to apples comparison.
3. both gain and SNR are important, but they are largely independent. Insufficient gain and you end up with quantisation noise and onion rings - too high a gain and you don't change the SNR, but can get saturation. So what is needed is enough gain to get above the onion rings and below saturation at high framerates and enough SNR to operate at high framerates without excessive noise. Different cameras can have different optimum operating points, so (again) comparing apples with apples is not so easy.
Have fun! Regards Ray